1. Technical Field of the Invention
The present invention broadly relates to a device for manufacturing a plastic lens. More particularly, the present invention relates to a device manufacturing the plastic lens by a casting method that uses active energy rays.
2. Description of Related Art
In manufacturing a plastic lens, a casting method is widely used. In the casting method, a plastic lens forming composition is injected into a casting mold. Then, the casting mold injected with the plastic composition is heated or irradiated by active energy rays such as ultraviolet rays, so that the plastic composition is polymerized and hardened. Subsequently, the casting mold is removed, whereby the plastic lens is obtained.
The method for curing (polymerizing and hardening) the lens forming composition by irradiating the active energy rays (an active-energy-ray irradiation polymerization method) completes the process of polymerization in a short period of time. In other words, polymerizing by irradiating the lens forming composition with active energy rays helps reduce the manufacture time resulting in faster delivery of the plastic lens. In particular, this method is suitable for producing a custom plastic lens or for producing a number of different types of plastic lenses in small quantities of each.
As disclosed in Japanese Unexamined Patent Application Publication No. 10-249953, a widely used method for manufacturing a plastic lens is the active-energy-ray irradiation polymerization method. In this method, ultraviolet rays are irradiated onto both surfaces or both faces of the casting mold injected with the plastic composition to polymerize or cure this injected composition, while the casting mold is transferred, by a transferring conveyer, into an ultraviolet irradiation furnace with an ultraviolet irradiation device disposed therein.
In the manufacturing method in which the composition is polymerized by the ultraviolet irradiation device while the casting mold is transferred by the transferring conveyer, a so-called consecutive ultraviolet hardening device is used. In this consecutive ultraviolet hardening device, the transferring conveyer is consecutively operated.
FIGS. 5 and 6 are a front view and a cross-sectional view showing the basic structure of the consecutive ultraviolet hardening device. In the consecutive ultraviolet hardening device 100, there is a supplying portion 102 for supplying the casting mold 101 to be polymerized, an ultraviolet irradiating portion 103 for irradiating the ultraviolet rays, a cooling portion 104 for cooling the casting mold 101 and a removing portion 105 for removing the polymerized casting mold 101. These portions 102-105 are arranged in linear fashion, for example, in a straight line as illustrated in FIGS. 5 and 6.
In addition, the consecutive ultraviolet hardening device 100 includes a transferring conveyer 106 as illustrated in FIGS. 5 and 6. The transferring conveyer 106 has a metallic transferring chain or a metallic belt 109 and a work chuck 110 (described in further detail below). As illustrated in FIGS. 5 and 6, this metallic transferring chain 109 is arranged on both sides of the casting mold 101 to be polymerized, as is known in the art, such that the ultraviolet lamps 107 and 108 of the ultraviolet irradiating portion 103 emit ultraviolet rays onto both surfaces of the casting mold 101. In particular, the ultraviolet rays are emitted onto the casting mold 101 via irradiating windows 111 and 112 illustrated in FIGS. 5 and 6. These irradiating windows are made of quartz glass. Alternatively, if the ultraviolet rays are emitted on only one surface or one face of the casting mold 101, the casting mold 101 will have to cope with the ultraviolet irradiation for a long period of time.
The transferring conveyer 106 also includes a metallic work chuck 110 that is integrally attached to the transferring chain 109. The work chuck 110 is constructed in a way which permits the casting mold 101 to be removably attached to the work chuck 110. The casting mold 101 is placed and held in the work chuck 110. The casting mold 101 held in the work chuck is then transferred on the consecutive ultraviolet hardening device from the supplying portion 102 up to the removing portion 105 in a direction illustrated by an arrow in FIGS. 5 and 6. During this transfer, the polymerization of the lens forming composition is performed.
However, in the method of manufacturing the plastic lens using the consecutive ultraviolet hardening device, since the hardening device is arranged in a linear fashion, the device is bulky. Besides, since the supplying portion and the removing portion of the casting mold are spaced apart from each other, an operator must travel from the supplying portion to the removing portion to obtain the cured lens forming composition. This traveling results in a time loss. In addition, since the casting mold with the injected plastic composition is transferred by the transferring conveyer and is gradually irradiated by the ultraviolet rays, it is necessary to carefully manage the ultraviolet irradiation energy. Further, there is a problem of a decrease with time in the irradiation intensity of the ultraviolet rays. In particular, the quartz glasses of irradiating windows 111 and 112 are polluted due to dust particles from the transferring conveyer 106 (in particular, the transferring chain 109), which results in decreasing the intensity of irradiation of the ultraviolet rays reaching the casting mold 101.